In the scenario where two different gases are held at the same pressure, volume, and temperature, the quantity that can differ between the two gases is:
the mass of each gas
This is because the mass of a gas depends on its molar mass, which varies between different gases. Since the gases have the same number of moles (according to the ideal gas law), but their molar masses are different, their masses will also differ accordingly.
The other options would not differ under those conditions:
- The gas constant is a property specific to each gas but does not affect the setup described.
- The number of moles of gas would be the same if pressure, volume, and temperature are the same.
- The molar volume of an ideal gas is the same at the same conditions of temperature and pressure, so it wouldn't differ either.